Field of the Invention
The present invention relates to a roller for electrophotography to be used in an electrophotographic image-forming apparatus (hereinafter, also simply referred to as “image-forming apparatus”), such as a copier or printer employing an electrophotographic system.
Description of the Related Art
An image-forming apparatus employing an electrophotographic system is mainly composed of an electrophotographic photosensitive member, a charging device, an exposure device, a developing device, a transfer device, and a fixing device.
Many charging devices employ a system of charging the surface of a photosensitive member by applying a voltage to a charging roller being in contact with or disposed in proximity to the surface of the photosensitive member. The charging roller being in contact with the surface of the photosensitive member and charging the photosensitive member is rotated following the photosensitive member.
Stabilization of the driven rotation of the charging roller needs a sufficient nip width between the charging roller and the electrophotographic photosensitive member. The nip width between the charging roller and the photosensitive member can be secured by reducing the hardness of the charging roller. Japanese Patent Laid-Open No. 2008-275656 discloses a method of reducing the hardness of a charging roller with a conductive foamed elastic layer. Japanese Patent Laid-Open No. 2001-254725 discloses a method for achieving a desired hardness by adding organic microballoons to an elastomer layer of a semiconductive roller.